Kink-free spiral-wound catheter

ABSTRACT

This invention is a surgical device. In particular, it is a catheter suitable for treating a tissue target within the body, which target is accessible through the vascular system. Central to the invention is the use of stiffener ribbons, typically metallic, wound within the catheter body in such a way as to create a catheter having controllable stiffness.

This application is a continuation of application Ser. No. 08/266,540filed Jun. 27, 1994 now U.S. Pat. No. 5,454,795.

FIELD OF THE INVENTION

This invention is a surgical device. In particular, it is a cathetersuitable for treating a tissue target within the body, which target isaccessible through the vascular system. Central to the invention is theuse of stiffener ribbons, typically metallic, wound within the catheterbody in such a way as to create a catheter having controllablestiffness.

BACKGROUND OF THE INVENTION

Catheters are increasingly used to access remote regions of the humanbody and, in doing so, delivering diagnostic or therapeutic agents tothose sites. In particular, catheters which use the circulatory systemas the pathway to these treatment sites are especially useful. Forinstance, it is commonplace to treat diseases of the circulatory systemvia angioplasty (PCTA) using catheters having balloons on their distaltips. It is similarly common that those catheters are used to deliver aradiopaque agent to that site prior to the PCTA procedure to view theproblem prior to treatment.

Often the target which one desires to access by catheter is within asoft tissue such as the liver or the brain. The difficulty in reachingsuch a site must be apparent even to the casual observer. The cathetermust be introduced through a large artery such as those found in thegroin or the neck and be passed through ever more narrow regions of thearterial system until the catheter reaches a selected site. Often suchpathways will wind back upon themselves in a multi-looped path. Thesecatheters are fairly difficult to design and utilize in that they mustbe fairly stiff at their proximal end so to allow the pushing andmanipulation of the catheter as it progresses through the body, and yetmust be sufficiently flexible at the distal end to allow passage of thecatheter tip through the loops and increasingly smaller blood vesselsmentioned above and yet at the same time not cause significant trauma tothe blood vessel or to the surrounding tissue. Further details on theproblems and an early, but yet effective, way of designing a catheterfor such a traversal may be found in U.S. Pat. No. 4,739,768, toEngelson. These catheters are designed to be used with a guidewire. Aguidewire is simply a wire, typically of very sophisticated design,which is the "scout" for the catheter. The catheter fits over and slidesalong the guidewire as it passes through the vasculature. Said anotherway, the guidewire is used to select the proper path through thevasculature with the urging of the attending physician and the catheterslides along behind once the proper path is established.

There are other ways of causing a catheter to proceed through the humanvasculature to a selected site, but a guidewire-aided catheter isconsidered to be both quite quick and somewhat more accurate than theother procedures. One such alternative procedure is the use of aflow-directed catheter. These devices often have a small balloonsituated on the distal end of the catheter which may be alternativelydeflated and inflated as the need to select a route for the catheter isencountered.

This invention is an adaptable one and may be used in a variety ofcatheter formats. The invention utilizes the concept of combining apolymeric tubing with one or one or more spirally wound ribbons tocontrol the stiffness of the resultant catheter body. This catheter maybe used in conjunction with a guidewire, but the catheter body may alsobe used as a flow-directed catheter with the attachment of a balloon orin combination with a specifically flexible tip, as is seen, forinstance, in U.S. application Ser. No. 08/023,805 to Zenzen et al., theentirety of which is incorporated by reference.

The use of ribbons in winding a catheter body is not a novel concept.However, none have used this concept to produce a catheter which has thephysical capabilities of the catheter of this invention.

Examples of previously disclosed catheters include U.S. Pat. No.2,437,542, to Crippendorf. Crippendorf describes a "catheter-typeinstrument" which is typically used as a ureteral or urethral catheter.The physical design is said to be one having a distal section of greaterflexibility and a proximal section of lesser flexibility. The device ismade of intertwined threads of silk, cotton, or some synthetic fiber. Itis made by impregnating a fabric-based tube with a stiffening mediumwhich renders the tube stiff yet flexible. The thus-plasticized tubingis then dipped in some other medium to allow the formation of a flexiblevarnish of material such as a tung oil base or a phenolic resin and asuitable plasticizer. There is no indication that this device is of theflexibility required herein. Additionally, it appears to be the typewhich is used in some region other than in the periphery or in softtissues of the body.

Similarly, U.S. Pat. No. 3,416,531, to Edwards, shows a catheter havingbraiding-edge walls. The device further has layers of other polymerssuch as TEFLON and the like. The strands found in the braiding in thewalls appear to be threads having classic circular cross-sections. Thereis no suggestion of constructing a device using ribbon materials.Furthermore, the device is shown to be fairly stiff in that it isdesigned so that it may be bent using a fairly large handle at itsproximal end. There is no suggestion to either merely wind ribbon onto apolymeric substrate to form a catheter or, in particular, to make one ofsuch flexibility as is required herein.

U.S. Pat. No. 4,484,586 shows a method for the production of a hollow,conductive medical tubing. The conductive wires are placed in the wallsof hollow tubing specifically for implantation in the human body,particularly for pacemaker leads. The tubing is made of, preferably, anannealed copper wire which has been coated with a body-compatiblepolymer such as a polyurethane or a silicone. The copper wire is coatedand then used in a device which winds the wire into a tube. The woundsubstrate is then coated with another polymer to produce a tubing havingspiral conducting wires in its wall.

A document showing the use of a helically wound ribbon of flexiblematerial in a catheter is U.S. Pat. No. 4,516,972, to Samson. Thisdevice is a guiding catheter and it may be produced from one or morewound ribbons. The preferred ribbon is an aramid material known asKevlar 49. Again, this device is a device which must be fairly stiff. Itis a device which is designed to take a "set" and remain in a particularconfiguration as another catheter is passed through it. It must be softenough so as not to cause substantial trauma, but it is certainly notfor use as a guidewire. It would not meet the flexibility criteriarequired of the inventive catheter described herein.

U.S. Pat. No. 4,806,182, to Rydell et al., shows a device usingstainless steel braid imbedded in its wall and an inner layer ofpolyfluorocarbon. The process also described therein is a wax tolaminate the polyfluorocarbon to a polyurethane inner liner so asprevent delamination.

U.S. Pat. No. 4,832,681, to Lenck, shows a method and apparatus forartificial fertilization. The device itself is a long portion of tubingwhich, depending upon its specific materials of construction, may bemade somewhat stiffer by the addition of spiral reinforcement comprisingstainless steel wire.

Another catheter showing the use of braided wire is shown in U.S. Pat.No. 5,037,404, to Gold et al. Mention is made in Gold et al of theconcept of varying the pitch angle between wound strands so to result ina device having differing flexibilities at differing portions of thedevice. The differing flexibilities are caused by the difference inpitch angle. No mention is made of the use of ribbon, nor is anyspecific mention made of the particular uses to which the Gold et al.device may be placed.

U.S. Pat. No. 5,069,674 shows a small diameter epidural catheter whichis flexible and kink-resistant when flexed. The wall has a compositestructure including a helical coil, typically stainless steel or thelike, a tubular sheath typically of a polymer, and a safety wire whichis spiraled about the coil and is often in the shape of a ribbon.

U.S. Pat. No. 5,176,660 shows the production of catheters havingreinforcing strands in their sheath wall. The metallic strands are woundthroughout the tubular sheath in a helical crossing pattern so toproduce a substantially stronger sheath. The reinforcing filaments areused to increase the longitudinal stiffness of the catheter for good"pushability". The device appears to be quite strong and is wound at atension of about 250,000 lb./in.² or more. The flat strands themselvesare said to have a width of between 0.006 and 0.020 inches and athickness of 0.0015 and 0.004 inches. There is no suggestion to usethese concepts in devices having the flexibility and otherconfigurations described below.

U.S. Pat. No. 5,178,158, to de Toledo, shows a device which is aconvertible wire having use either as a guidewire or as a catheter. Thecoil appears to be a ribbon which forms an internal passage through thecoil/catheter device. No interior coating is applied.

U.S. Pat. No. 5,217,482 shows a balloon catheter having a stainlesssteel hypotube catheter shaft and a distal balloon. Certain sections ofthe device shown in the patent use a spiral ribbon of stainless steelsecured to the outer sleeve by a suitable adhesive to act as atransition section from a section of very high stiffness to a section ofcomparatively low stiffness.

None of these devices are catheters which have the critical benddiameter required herein, nor do they have the compression strength, orflexibility of the present invention.

SUMMARY OF THE INVENTION

This invention is a catheter section made up, desirably, of an innertubing liner, one or more spirally wound stiffener ribbons, and an outercovering. The inner tubing liner, when used, typically is a polymericsection of tubing which may be a thermoplastic and is miscible uponheating with the material found in the outer covering. The inner layermay be a thermosetting material which adheres to the outer material orwhich may be adhesively bound to the outer material. In any event, thetwo or more polymeric layers are to hold the spirally wound stiffenerribbons in place in the catheter assembly.

The stiffener ribbon may be wound onto the inner tubing liner in anumber of different ways. It may be, in its most basic form, a singlestrand of ribbon wound in a single direction. It may a number of ribbonsof differing sizes and compositions wound each way around the tubingliner. The ribbons are typically metallic but may be of other materials.

The various catheter sections may be formed into an integral catheterassembly. Wise choices of materials permit the catheter to be of asmaller overall diameter with a superior critical diameter. The cathetermay be designed to integrate lubricious materials into the base designof a particular catheter product without adding extraneous thickness andstiffness. The catheter may be wholly constructed of materials which arestable to radioactive sterilization procedures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows, in side view, a typical three section catheter.

FIG. 2 shows, in magnification, a section of the inner portion of oneinventive section of this catheter.

FIG. 3 shows, in magnification, a section of the inner portion of thiscatheter.

FIGS. 4, 5, and 6 show fragmentary, cross sectional views of variousconfigurations of the inner sections of multi-section catheters madeaccording to this invention.

FIG. 7 shows, in cross-section, a typical catheter section madeaccording to this invention.

FIG. 8 shows a fragmentary cross-sectional view of a catheter sectionmade according to this invention.

FIGS. 9A and 9B show details of the method of testing the "critical benddiameter" of this invention.

FIGS. 10 and 11 show highly desirable embodiments, in fractionalcross-section, of multi-section catheters made according to thisinvention.

DESCRIPTION OF THE INVENTION

This invention is a kink-resistant catheter section or catheter. It is acomposite device having at least one section including a helically woundribbon stiffener coaxially incorporated into that section or sections.The catheter is configured so that at least the distal portion of thecatheter has a critical bend diameter of no more than 3.5 mm, preferablyno more than 2.5 mm, and most preferably no more than 1.5 mm.Additionally, that section desirably has a lateral stiffness, such aswould be measured by a Tinius-Olsen Stiffness Tester, of at least 6,500°of deflection/inch-pound (measured at 20°-30° of deflection, 0.005 lb,over a 0.25" span), preferably 7,500° of deflection/inch-pound, and mostpreferably 9,500° of deflection/inch-pound. We have additionally foundthat the radial compression strength of the section is quite high ascompared to other distal sections found on comparable catheter distalsections.

A typical multi-section catheter (100) which may incorporate theconcepts of this invention is shown in FIG. 1. Such a catheter isdescribed in more detail in U.S. Pat. No. 4,739,768, to Engelson, (theentirety of which is incorporated by reference) and is suitable forneurological and peripheral vascular applications. Clearly, then, it isalso suitable for less demanding service such as might be encountered inaccess and treatment of the heart. One difficulty which has arisen ashigher demands for length have been placed on these catheters is thatthe diameter of the distal section necessarily becomes smaller andsmaller. This is so since the longer catheters must reach ever moresmaller vascular areas. This smaller diameter requires a concomitantthinning of the wall section. The thinner section walls may kink orripple when actively pushed along the guidewire or when vasoocclusivedevices are pushed through the catheter's lumen. The typicalconfiguration shown in FIG. 1 has a distal section (102) havingsignificant flexibility, an intermediate section (104) which istypically less flexible, and a long proximal section (106) which in turnis least flexible. The distal section (102) is flexible and soft toallow deep penetration of the extraordinary convolutions of theneurological vasculature without trauma. Various known and necessaryaccessories to the catheter assembly, e.g., one or more radiopaque bands(108) at the distal region to allow viewing of the position of thedistal region under fluoroscopy and a luer assembly (110) for guidewire(112) and fluids access, are also shown in FIG. 1. The typicaldimensions of this catheter are:

Overall length: 60-200 cm

Proximal section (106): 60-150 cm

Intermediate Section (104): 20-50 cm

Distal Section (102): 2.5-30 cm

Obviously, these dimensions are not particularly critical to thisinvention and are selected as a function of the malady treated and itssite within the body. However, as will be discussed below, use of thespiral wound ribbon permits the walls of the catheter to be somewhatthinner with no diminution of performance, e.g., crush strength orflexibility, or indeed, an improvement in performance.

FIG. 2 shows a magnified section of a catheter body or section (200)showing the most basic aspects of one variation of the invention. Asshown there, the catheter body or section has an inner tubing member(202) and a helically wound ribbon (204). The inner tubing member (202)may, depending on the section of the catheter, be of any of a variety ofpolymers, variously stiff or flexible. For instance, if the section(200) is used as a proximal section, the inner tubing (202) may be apolyimide, polymides such as the Nylons, high density polyethylene(HDPE), polypropylene, polyvinylchloride, various fluoropolymers (forinstance: PTFE, FEP, vinylidene fluoride, mixtures, alloys, copolymers,block copolymers, etc.), polysulfones or the like. Blends, alloys,mixtures, copolymers, block copolymers, of these materials are alsosuitable, if desired.

If a more flexible section is required, the inner tubing member (202)may be a polyurethane, low density polyethylene (LDPE),polyvinylchloride, THV, etc. and other polymers of suitable softness ormodulus of elasticity.

We have also found that this catheter design allows us to use in thedistal portion of the catheter, thin-walled tubing of inherently moreslippery polymers, such as PTFE and FEP and their mixtures, which havethe benefit of being lubricious but otherwise would have been used in asomewhat greater thickness. Clearly, greater thickness tubing of thesepolymers results in the tubing being somewhat stiffer. The wallthickness of the inner tubing liner (202) may be as thin as 0.5 mil andas thick as 10 mil, depending upon catheter usage, portion of thecatheter chosen, polymer choice, and the style of catheter. Typicalchoices for inner tubing liner polymers would be:

    ______________________________________                                                      Example    Wall Thickness                                       Catheter Section                                                                            Polymer    (mil)                                                ______________________________________                                        Distal        Polyethylenes                                                                            0.5-3                                                              Fluoropolymer                                                                            0.5-3                                                              s          0.5-3                                                              Polyurethane                                                    Intermediate  Polyethylenes                                                                            1-4                                                                Fluoropolymer                                                                            1-4                                                                s          1-4                                                                polyolefin 1-4                                                                blends                                                                        Polypropylene                                                   Proximal      LDPE/HDPE  1-4                                                                Polypropylene                                                                            1-4                                                                Fluoropolymer                                                                            1-4                                                                s          1-4                                                                Polyimide                                                       ______________________________________                                    

These dimensions are obviously only ranges and each catheter variationmust be carefully designed for the specific purpose to which it isplaced.

Preferred combinations of polymers for catheter configurations will alsobe discussed below. It should also be noted at this point that each ofthe polymers discussed herein may be used in conjunction with radiopaquematerial such as barium sulfate, bismuth trioxide, bismuth carbonate,powdered tungsten, powdered tantalum, or the like so that the locationof the various pieces of tubing may be radiographically visualizedwithin the vessel.

The spiral wound ribbon (204) shown in FIG. 2 may also be of a varietyof different materials. Although metallic ribbons are preferred, becauseof their strength-to-weight ratios, fibrous materials (both syntheticand natural) may also be used. Preferred, because of cost, strength, andready availability are stainless steels (308, 304, 318, etc.) andtungsten alloys. Also acceptable, but with a penalty variously instrength, density, and ductility, are precious metals such as gold,platinum, palladium, rhodium and the like, as well as alloys of thesemetals. Alloys of many of these precious metals with, for instance,tungsten, have lower ductility than the neat precious metal.

The class of alloys known as super-elastic alloys is also a desirableselection, although the processability of these alloys into smallribbons is not routine. Preferred super-elastic alloys include the classof materials known as nitinol--alloys discovered by the U.S. NavyOrdnance Laboratory. These materials are discussed at length in U.S.Pat. Nos. 3,174,851 to Buehler et al., 3,351,463 to Rozner et al., and3,753,700 to Harrison et al. These alloys are not readily commerciallyavailable in the small ribbons required by the invention described here,but for very high performance catheters are excellent choices.

Metallic ribbons (204) that are suitable for use in this invention aredesirably between 0.75 mil and 1.5 mil in thickness and 2.5 mil and 8.0mil in width. For superelastic alloys, particularly nitinol, thethickness and width may be somewhat finer, e.g., down to 0.5 mil. and1.0 mil., respectively. Currently preferred, based on strength, cost andavailability are stainless steel ribbons of 1 mil.×3 mil., 2 mil.×6mil., and 2 mil.×8 mil.

Suitable non-metallic ribbons include those made of polyaramids (e.g.,KEVLAR), carbon fibers, and lower performance polymers such as Dacronand the Nylons. Acceptable natural fibers include silk and cotton. Itshould be observed that the preferred manner of using non-metallicribbons in this invention is in combination with metallic ribbons toallow "tuning" of the stiffness of the resulting composite or as anopposite "handed" ribbon in the composite to lessen the tendency of themetallic ribbon to unwind and hence create bumps or constructions in thecatheter lumen.

Returning to FIG. 2, the stiffener ribbon (204) may be simply wound ontothe inner tubing liner (202). Depending upon the choice of materials forinner tubing liner (202), the stiffener ribbon (204) may be applied withan adhesive. The adhesive is used primarily to cause the outer cover(discussed below) to adhere to the inner tubing liner (202). We preferto choose polymers for the components of the catheter which inherentlyadhere to each other, e.g., certain polyethylenes and polyimides, orthermoplastics, which are miscible with each other upon appropriateheating, e.g., PEBAX and polyurethanes. When we construct a cathetersection using only the materials found in the respective tubingsections, or using a third material to improve the miscibility of thematerials found in the respective liners and cover, we refer to thatconstruction as being "binderless." If an adhesive is used to promotethe adherence and outer layer to an inner layer, that would not be"binderless."

Thermoplastics which are inherently adherent to each other or aremiscible with each other are preferred in the intermediate and distalareas of the catheter since the noted adhesives may then be omitted andthe various stiffener ribbons held in place by the junction of the innertubing liner (202) and the outer cover (not shown in this Figure).

The wound inner sector shown in FIG. 2 incorporates a helically woundstiffener ribbon (204) wound in one direction or "hand". FIG. 3 shows asecond stiffener ribbon (206) wound in a second direction or"handedness" around both the first stiffener ribbon (204) and the innertubing liner (202).

For economies of production, it is desirable to "gang-wind" the ribbonstiffeners onto the inner tubing liner. That is to say, for instance,that a catheter having a primary or first stiffener ribbon (204) with aspacing of twelve turns per inch can be produced by turning the cathetertubing twelve times and wrapping a single ribbon about it or by turningthe catheter tubing six times and wrapping a pair of stiffener ribbonsspaced apart so to produce a device appearing to have twelve turns ofribbon thereon. Similarly, the inner tubing can be turned four timeswith a gang-wind of three ribbons, etc. As will be discussed below, noneof the wound ribbons of necessity must be of a consistent size. Eachstiffener ribbon on each section of the catheter assembly may be of adifferent width and thickness.

A further aspect of this invention is shown in FIG. 4. The catheter(210) has three discrete sections: a proximal section (212), anintermediate section (214) and a distal section (216). This catheter(210) is analogous in overall function to that shown in FIG. 1. Inparticular, the proximal section (212) of the catheter is stiffest inthat the number of stiffener ribbons (218) are wound onto the tubularsubstrate is densest. The distal portion (216) is wound to the otherextreme in that the number of stiffener ribbons (218) is least dense.The intermediate section (214) is wound with stiffener ribbons to adensity intermediate between the two adjacent sections. As has beennoted elsewhere, although the majority of instances noted herein discussthree-section catheters, the invention is not so limited. The inventivecatheters may have fewer or may have more sections depending upon theultimate use to which the catheter is placed.

The FIG. 4 catheter sections are shown using stiffener ribbons in eachsection of the same size. The various stiffener ribbons are of the samesize in each direction of wind as well. The density of turns is one wayin which to control the overall stiffness of the catheter section.

Another method for controlling stiffness is shown in FIG. 5. As was thecase with the catheter shown in FIG. 4, a three piece catheter (220) isshown. In this instance, however, the manner of controlling thestiffness is different. In this embodiment, the width of the respectivestiffener ribbons is varied to acquire the specific desired stiffness.For instance, in catheter assembly (220), the proximal portion (222)uses comparatively wide stiffener ribbons (228) shown wound in bothdirections. Intermediate section (224) utilizes narrower stiffenerribbons (230) and distal section (226) uses the narrowest stiffenerribbons (232).

Although, again, each section is portrayed as having ribbons of equalsize, wound in each direction, such is obviously not a requirement ofthe invention.

The width of the ribbons may be chosen in such a way that differentsizes are wound in different directions or multiple sizes of stiffenerribbon may be gang-wound in the same direction or, obviously, acombination of these themes are also appropriate.

FIG. 6 shows a three-part catheter to (240) also having an exempletivethree-part construction: proximal section (242), intermediate section(244) and distal section (246). In this configuration, the proximalsection (242) utilizes both wide stiffener ribbons (248) and narrowstiffener ribbons (250) in one wind direction and only narrow stiffenerribbons (252) in the other wind direction. The intermediate sector (244)uses the same collection of ribbons in each wind direction:specifically, two narrow ribbons (254) and a single wide ribbon (256).The distal section (246) utilizes but a single width of ribbon (258) ineach wind direction. This drawing depicts the wide variation in"tuning," the stiffness of the catheter sections for particular purposesby use of varied spacing of the stiffener ribbon winding, the use ofvarious width ribbons, as well as the use of combinations of ribbonwidth.

Once the stiffener ribbon is wound onto the inner tubing liner, an outercovering must then be applied.

FIG. 7 shows, in cross-section, a section of (270) of catheter having aninner tubing liner (272), a stiffener ribbon (274), and an outer cover(276). The outer cover or layer may be applied in a variety of ways. Asnoted above, the preferred way is to shrink an appropriate tubing ontothe stiffener ribbon and continue to shrink the tubing in such a waythat it fills the interstices between windings of the stiffener ribbon(274) as is shown in FIG. 7. This allows the outer covering (276)directly to contact the inner tubing liner (272). Even more desirably,the outer tubing (276) should be further heated to allow mixing of theouter covering (276) with the inner tubing liner (272) at theirinterface so as to form a strong integral catheter section (270). If thetwo polymer layers are mixed at this interface, so much the better forthe strength of the bond.

It should be apparent that the outer layer (276) may also be applied bydipping the inner tubing layer (272)/stiffener ribbon (274) into amolten polymer bath or into a polymer dissolved in a solid or into asuspension or latex comprising the outer cover polymer. Obviously, thecover may be placed on the catheter by spraying or otherwise applyingthe material. Included in such a class are the polyurethanes,polysilicones, polyvinylpyrrolidone, etc.

The catheter and catheter sections of this invention may be coated orotherwise treated to increase their lubricity.

FIG. 8 shows another variation of the inventive catheter body in whichthe inner polymeric layer is eliminated. The section is quite simple inconstruction. Specifically, an outer layer of a polymeric material (280)is placed over a previously wound coil (282). These outer layers maypreferably be made of a heat shrinkable tubing having a thin wallthickness. Polyethylenes, polyurethanes, polyvinylchloride,polyfluoroethylenes, and blends or copolymers containing such polymers(e.g., THV) are especially preferred.

The FIG. 8 variation, when used with a coil (282) wire or ribbon havinga pitch selected to provide spacing between adjacent turns of the coil,is especially useful as a distal or midsection of a catheter in that itis quite flexible, retains kink resistance, and is quite easy toconstruct.

As was noted above, the most distal portion of the distal section ofthis catheter (and preferably other sections as well) have a criticalbend diameter of no more than 3.5 mm, preferably no more than 2.5 mm,and most preferably no more than 1.5 mm. Additionally, that sectiondesirably has a lateral stiffness, such as would be measured by aTinius-Olsen. Stiffness Tester, of at least 6,500° ofdeflection/inch-pound (measured at 20°-30° of deflection, 0.005 lb, overa 0.25" span), preferably 7,500° of deflection/inch-pound, and mostpreferably 9,500° of deflection/inch-pound.

The test we utilize for critical bend diameter determination uses a testshown schematically in FIGS. 9A and 9B.

In general, as shown in FIG. 9A, a catheter section (300) is placedbetween two plates (desirably of plastic or glass or the like forvisibility) and often with an optional peg (302) to hold the cathetersection (300) loop in place. The ends of the catheter are then pulleduntil a kink appears in the body of the catheter. Alternatively, theratio of the outer diameters (major diameter:minor diameter) as measuredat apex (304) reaches a value of 1.5. FIG. 9B shows the cross section ofthe catheter sector at (304) and further shows the manner in which themajor diameter and the minor diameter are measured. These two methodsprovide comparable results although the latter method is morerepeatable.

Many times herein, we refer to the "region" section of the catheter.Where the context permits, by "region" we mean within 15% of the pointspecified. For instance, "the distal region of the distal section" wouldrefer to the most distal 15% in length of the distal section.

Two highly desirable catheter designs are shown in FIGS. 10 and 11, infragmentary cross-section. In particular, FIG. 10 shows a catheterhaving two sections of different stiffness. The proximal section (320)is made up of an inner tubing liner (322) of polyimide, a spiral woundstiffener ribbon (324) of 1 mil.×3 mil. stainless steel, and an outercovering (326) of shrink wrap FEP-vinylidene fluoride (THV-200). Thedistal section (328) shares the same outer covering (326) but also hasan inner tubing liner (330) of FEP-vinylidene fluoride (THV-200). It maybe observed that the spacing between the winds of stiffener ribbon (326)is quite different in the two sections, The proximal section has atwelve turn per inch spacing but the distal section has a wind spacingof only four turns per inch.

FIG. 11 shows a three flexibility sector catheter (340) with a proximalsection (342), an intermediate section (344), and a distal section(346). The proximal section is made up of an inner liner (348) of FEP; aspiral-wound 1×3 millimeter stainless steel ribbon (350) of twelve turnsper inch spacing is turned each way on the inner liner; and an outerlayer of FEP-vinylidene fluoride (THV-500).

The intermediate section (344) includes an extension of the proximalinner liner (348) found in the proximal section (342) and an outerdistal section (354). The outer distal covering (354) may also be of FEP(but of a somewhat softer makeup than the proximal inner liner (348))but preferably is of a FEP-vinylidene fluoride such as THV-200. The FEPand FEP-vinylidene copolymer are miscible when heated. The wind-spacingin this section has been spread out to a spacing of nine turns per inch.

Finally, the distal section (346) is made up of an extension of theouter distal section (354) and an inner distal tubing (356). In thiscase, the inner distal section is of the same material as that of theouter distal section (356). The wind-spacing in this section has beenspread out to a spacing of six turns per inch.

This invention has been described and specific examples of the inventionhave portrayed. The use of those specifics is not intended to limit theinvention in any way. Additionally, to the extent that there arevariations of the invention which are within the spirit of thedisclosure and yet are equivalent to the inventions found in the claims,it is our intent that this patent cover those variations as well.

I claim as my invention:
 1. A catheter section comprising:an elongatetubular member having a proximal end and a distal end and a passagewaydefining an inner lumen extending between those ends, said elongatetubular member comprising an outer tubular cover in coaxial relationshipwith at least a first ribbon stiffener comprising a superelastic alloyand having a handedness and spirally and coaxially wound and covered bysaid outer tubular cover, and the catheter section, in the region of thedistal end, has a critical bend diameter of no more than 3.5 mm.
 2. Thecatheter section of claim 1 wherein the section has a lateralflexibility of greater than 6500°/in-lb.
 3. The catheter section ofclaim 1 further comprising an inner tubular liner located coaxiallywithin said at least first ribbon stiffener.
 4. The catheter section ofclaim 1 where the catheter section additionally comprises a secondribbon stiffener of opposite handedness to the first ribbon stiffenerspirally and coaxially wound upon said first ribbon stiffener.
 5. Thecatheter section of claim 1 additionally comprising at least oneadditional ribbon stiffener having the same handedness as the firstribbon stiffener.
 6. The catheter section of claim 1 where the elongatetubular member has at least one region of variable stiffness between theproximal end and the distal end.
 7. The catheter section of claim 1where the first ribbon stiffener has a pitch which varies between theproximal end and distal end.
 8. The catheter section of claim 4 wherethe second ribbon stiffener has a pitch which varies between theproximal end and distal end.
 9. The catheter section of claim 3 wherethe outer tubular cover compresses materials selected from the groupconsisting of polyimide, polyamides, polyethylene, polypropylene,polyvinylchloride, fluoropolymers including PTFE, FEP, vinylidenefluoride, and their mixtures, alloys, copolymers, and block copolymers,polysulfones or the like.
 10. The catheter section of claim 3 where theinner liner compriseses a material selected from polyurethane, lowdensity polyethylene (LDPE), polyvinylchloride, fluoropolymers includingPTFE, FEP, vinylidene fluoride, and their mixtures, alloys, copolymers,and block copolymers.
 11. The catheter section of claim 1 where thefirst ribbon stiffener comprises a ribbon having a thickness between0.75 mil and 2.5 mil and a width between 2.5 and 8.0 mil.
 12. Thecatheter section of claim 5 where the at least one additional ribbonstiffener comprises a ribbon having a thickness between 0.75 mil and 2.5mils and a width between 2.5 and 8.0 mils.
 13. The catheter section ofclaim 1 where at least one of the liner and cover materials areradiopaque.
 14. The catheter section of claim 1 where the at least afirst ribbon stiffener comprises a nickel-titanium alloy.
 15. Thecatheter section of claim 4 where the at least a second ribbon stiffenercomprises a nickel-titanium alloy.
 16. The catheter section of claim 3where the inner tubular liner comprises a fluorocarbon polymer.